1. Field of the Invention
The present invention relates to the field of human and animal health and in particular to vaccination approaches for control of Trypanosoma cruzi infection and Chagas disease. The present invention also relates to diagnosis of Trypanosoma cruzi infection and provides composition and methods for detecting Trypanosoma cruzi infection and evaluating efficacy of treatments against T. cruzi. 
2. Description of the Related Art
American trypanosomiasis or Chagas disease caused by Trypanosoma cruzi infection is the prime cause of death in young adults in endemic areas of the American continent and results in over 50,000 deaths, 1 million new cases, and loss of 2.74 million disability-adjusted years per year.
The prevalence rate of T. cruzi infection in dogs may reach up to 84%, determined by serological procedures and xenodiagnosis, in endemic areas (e.g. rural Argentina, Chiapas state of Mexico) [1, 2]. Dogs are the most frequent blood meal source for the domestic triatomines (T. barberi and T. pallidipennis in Mexico [3], T. infestans in Argentina [2]). Likewise, a high prevalence of seropositive dogs [4-6] and infected triatomines is routinely noted in rural and urban developments in southern US states [4, 7, 8] and suggested to maintain T. cruzi transmission in the human habitat. Triatomines are several times more likely to take their blood meal from dogs than from humans. The ratio of dog blood meals to human blood meals in the engorged guts of triatomines is estimated to be 2.3-2.6 times the ratio of the number of dogs to the number of humans in a household [9]. Thus, the probability of infecting an insect in one blood meal from dogs is estimated to be 200 times higher compared to the probability from adult humans [2]. These studies conclude: a) dogs are important host blood sources for domiciliary triatomines, b) the risk of T. cruzi infection in humans is increased by the presence of infected dogs, and c) strategies that can limit T. cruzi infection in the reservoir host would be effective in interrupting the parasite transmission to the vector, and consequently, to the human host.
The mathematical models based on epidemiological data suggest that vector control would be the most effective strategy against T. cruzi transmission [10]. However, sustained vector control, followed by constant surveillance, requires large-scale insecticide spraying every year that is not cost-effective and affordable for developing countries. Concerns also remain that insecticide use in the long-term may not be efficacious in blocking T. cruzi transmission, owing to the development of drug resistance by triatomines and reinfestation of homes by secondary sylvatic vectors, e.g., Triatoma sordida, in Brazil and other South American countries [11]. The same epidemiological models indicate that dog vaccination would be the second most efficient approach.
The efforts towards vaccine development are numerous. Based upon numerous studies in animal models, a successful vaccine that can provide protection from T. cruzi infection is envisioned by the research community to be composed of defined antigens capable of inducing strong neutralizing and lytic antibody response and type 1-biased T cell responses. Yet currently no vaccine is available for control of T. cruzi infection and disease development in humans and dogs.
Another major concern is the >300,000 infected individuals that have migrated to the US [25] (or other developed countries [26-27]) who can potentially transfer infection through blood or organ donation [28-29]. It is important that the migrant workforce in the US and the 20 million infected individuals living in the endemic countries [30] are diagnosed so as to prevent contamination of the donor blood banks. In the U.S., Ortho T. Cruzi ELISA Test System is licensed and approved by FDA for screening the donor blood samples. The Ortho System utilizes crude antigen preparation and there is a concern that crude antigen may exhibit cross-reactivity with antibodies to other parasitic protozoans (e.g. Leishmania, Trypanosoma rangeli) due to significant homology in the genome.
Thus, there is a recognized need in the art for a vaccine, a diagnosis composition and a treatment for control of T. cruzi infection and disease development in humans and dogs. The present invention fulfills this long-standing need and desire in the art.